Carbon-boron surfaced carbon filament

ABSTRACT

A high strength composite filament suitable for use as a reinforcement in metal matrices comprises a filamentary carbon substrate having a continuous essentially amorphous carbon alloy coating adhered thereto, the coating consisting essentially of approximately 43-60 atomic percent carbon, remainder boron.

United States Patent Galasso et al.

[ 1 Feb. 18, 1975 CARBON-BORON SURFACED CARBON 3,131,089 4/1968 Grulke etal ll7/228 3223832 2113 ili 135132 l "is C a t i ii [75] Inventors: Francis 8- Galasso, M h r; 3,671.306 6/1972 A1551 r. ll7/l0b Richard D. Veltri, Hartford, both of Conn.

Primary Examiner-Charles E. Van Horn [73} Assignee: Billiard Alreraft Corporation, East Asst-am Examinepqk w Massie Conn Attorney, Agent. or Firm-John D. Del Ponti l22| iilutl: Feb. 24, 1972 [2| I Appl. No.1228,953

[57] ABSTRACT F 16 3 A high strength composite filament suitable for use as [5]] [m Cl "/08 a reinforcement in metal matrices comprises a fila- [58] Fieid Cc)? l mentary carbon substrate having a continuous essen- 117/228 H5 111 b tially amorphous carbon alloy coating adhered H 69 led/Mi 5 6 3l3/341' thereto, the coating consisting essentially of approximately 43-60 atomic percent carbon, remainder bo- [56] References Cited UNITED STATES PATENTS 6 Claims, 2 Drawing Figures 1,019,391 3/l912 Wcintraub 117/228 PATENTEU 3 1975 F76. Z i

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BACKGROUND OF THE INVENTION In the evolution of filamentary composites, the devclopment of high modulus, high strength carbon yarns has evoked considerable interest. The major utility for these fibers for reinforcement. however, has been limited to the nonmetal, i.e.. resin, matrix materials. Commercially available carbon and graphite fibers which exhibit high tensile strength (over |50.000 psi) and Youngs Modulus (over 20 X l psi) are typically less than l0 microns in diameter and are well suited for use as reinforcement for the resin matrices. It is recognized. however, that the incorporation of metals into oriented carbon fibers imposes a more stringent set of requirements than does resin impregnation.

In order to effectively utilize carbon filament as reinforcement in metal matrix material, a relatively large diameter carbon fiber. coated with a diffusion barrier, is necessary. One of the paramount problems in obtaining carbon filamentreinforced metal matrix composites of acceptable properties can be attributed to the small size of the reinforcing carbon fibers. To achieve the maximum strengthening effect in a fiber-reinforced article. it is necessary to utilize filaments having a diameter substantially greater than the presently available l0 micron carbon fibers and more particularly having a final diameter greater than approximately 2 mils. It will be appreciated that filaments smaller than 2 mils. such as the [1. carbon fibers, for example, present problems in proper and complete matrix infiltration, susceptibility to chemical attack and lack of resistance to compressive forces normal to their axes. To offset the effects ofreactivity between the fiber and the metal matrix material. it is necessary to provide a barrier coating without, however, degrading the. structural properties of the substrate filament.

SUMMARY OF THE INVENTION The present invention relates to carbon-base filaments and, more particularly, to carbon-base monol'ilaments at least two mils in diameter suitable for use as reinforcement for metal matrix composites.

The present invention contemplates the production of a high strength. high modulus composite filament comprising a carbon filamentary core at least one mil in diameter, preferably l to 2 mils in diameter. having an adherent continuous essentially amorphous coating consisting essentially of a carbon-boron alloy consisting of approximately 43-60 atomic percent carbon. remainder boron. It has been found that such a carbonboron alloy coating composition. to a thickness of approximately 2 mils, will not only provide a diffusion barrier to the carbon and metal matrix materials but, in addition, will impart high strength and modulus thereto.

The present invention also contemplates the method for making such a filament and. in general. comprises continuously passing a carbon filament through a reactor, heating the filament to 1050l250C and exposing the heated filament to a reactant gas mixture consisting essentially of methane, boron trichloride and hydrogen. the mass flow ratios of methane/boron trichloride and hydrogen/boron trichloride being l.l6 to 8.08 and 0.5 to 2.0 respectively.

BRIEF DESCRIPTION OF THE DRAWINGS An understanding of the invention will become more apparent to those skilled in the art by reference to the following detailed description when viewed in light of the accompanying drawings. wherein:

FIG. I is a simple sketch, taken in elevation. of apparatus used in the production of the carbon-boron alloy coating of the carbon filaments of the present invention; and

FIG. 2 is an enlarged cross-sectional view through one of the filaments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As seen in FIG. I, the carbonboron alloy coating is produced on a resistively heated carbon monofilament 4 which is drawn downwardly through a reactor 6 comprising a tubular containment vessel 8, having a gas inlet I0 at the upper end of the reactor and a single exhaust port 12 at the lower end thereofv A reactant gas mixture consisting essentially of methane. boron trichloride and hydrogen is fed to the reactor through inlet I0. The containment vessel may be formed of Py rex. although a number of other materials including Vycor and quartz will be found satisfactory. The gas inlet 10 and the exhaust l2 penetrate and are elcctrically connected to the metallic end plugs 14 and [6 which provide the end closures for the containment vessel and also provide convenient means by which power may be supplied to the wire for resistance heating purposes.

The end plugs are each respectively provided with a well 20 and 22. for containing a suitable conductive sealant 24, such as mercury. which serves the dual pur pose of providing a gas seal around the wire where it penctrates the and plugs. and further providing electrical contact between the moving wire and the respective end plugs which are in turn electrically connected through the tubes 10 and I2 and the leads 26 and 28 to a suitable DC power source 30. The upper plug I4 is provided with a peripheral groove 34, which communicates with the mercury well 20 through the passageway 36, to provide peripheral sealing around the plug. Sealing between the end plug 16 and the lower end of the containment vessel 6 is provided by mercury contained in an annular well 38.

The respective plugs are each formed with a centrally oriented orifice 40 and 42 which is large enough to accommodate the free passage ofthe wire 2 thercthrough but which, in combination with the wire. is small enough to retain the mercury, through surface tension forces. in their respective wells.

The hydrogen is considered necessary in the reactant mixture since it acts not only as a coolant for the end plugs I4 and I6 but also acts to even temperature distribution and to catalyze the methane reaction. In practice, the relative proportions. expressed in flow rate ratios of the constituent methane and boron trichloride gases are critical to the formation of useful filaments. It is considered, for example. that with the hydrogcn/- boron trichloride ratio in the range of0.5 to 2.0, preferably at 1.0, the methane/boron trichloride ratio must be greater than l0 but less than approximately l0, preferably [.16 to 8.08. and optimally 2.34. At a mass flow ratio of methane/boron trichloride of 1.0 carbonboron deposition resulted in embrittled filaments which could not be handled without breaking.

By utilizing various gas flow ratios, relative amounts of carbon/boron in the coating layer may be varied. At the optimum ratio. monofilaments with a coating of C(52 percent B) had an average tensile strength of 265,000 psi and Young's Modulus of 4l l psi. As shown in FIG. 2, passage through the reactor results in a composite filament comprising a filamentary carbon core 46 having a relatively thick adherent coating of essentially amorphous carbon-boron 48. The term essentially amorphous" for purposes ofthe present inven tion is intended to mean that degree ofamorphousness which is represented by the appearance of one or two utilizing 1900 volts and I40 milliamps at a power setting of 252 watts to a temperature of llC while moving through the reactor at a rate of 40 ft/hr and achieved a final diameter of 3.3 mils. Several runs were made and the average UTS of this filament was in Example l except that substrate filament speed was ft/hr and a substrate temperature of l00C was ohs carbon reflecuo s1 t fraction stud t I: i i fzfi i tamed by 2 l 00 volts. I20 milltamps and 252 watts. The bon bong g 3 g: g g coated filament had a diameter of 3.2 mils and the ary f d c n erage UTS was I53.00U psi. The quality and composibonded to the desired matrIx materIal by such standard non of the coatIng was the same as In Example I. technlques as plasma spray, lIquId InfiltratIon or pow- 20 der metallurgy and braze or diffusion bonding. EXAMPLES 3-l l Various process techniques and parameters may be In the reactor apparatus of Example I, a CHJBCL, utilized in producing filaments ofthe presentinvention. ratio of 4.97 and an H /BCI ratio of 1.0 was mainas indicated by the following examples. The filamentained by a methane gas flow of538 cc/min. a BCl gas tary carbon substrates utilized were carbon monofilaflow of I08 cc/min and an H gas flow of 108 cc/mm. ments commercially available from Great Lakes Car- All of the coatings consisted of adherent essentially bon and. although of varying diameters as indicated in amorphous carbon-boron alloy having a composition at the examples. all exhibited an average UTS of 150.000 55 atomic percent C. 45 percent 8. The conditions and psi Young's Modulus of 4.8 X l0 psi. results are given in the following table.

TABLE I C'H IBCI Ratio at 4.97

Final A Current Voltage Power Temp, Substrate Diam Speed UTS Ex (ma) (voltsI (walls) (Cl Dianilmil) (mil) (ft/hr) (psi) 3 1211 2050 340 I130 loN .1.) Issouo 4v 140 1x1 10 253 1105 do. 3 i 011. 100.000 5 H10 I050 264 llj ll do. -l.(| Lin. IXLUUU e 160 1:150 2% 11.10 do 3.4 .10 lttsuoo 7 160 1x25 29: l I05 r10 4.] do. lt 2.(lt)(l 8 140 I900 3m l I ll) do. 4.0 do. 225.000 9 140 I900 266 do. 40 d0. l8ll.000 I0 90 I600 I44 I095 I 36 3.0 40 1240.000 ll I00 1550 I55 11-40 do. 3.1 do. 156.000

EXAMPLE l EXAMPLES 12-27 ln a reactor of the type illustrated utilizing a 24 inch [11 the reactor apparatus of Example l. a CH IBCI long reactor formed from l2 mm Pyrex tubing and a ratio of 2.34 and an H /BCl ratio of l.(l was mainreactant gas mixture of methane. boron trichloride and taincd by a methane gas flow of 407 cc/min. a BCl; gas hydrogen. a carbon-boron alloy coating was produced flow of I74 cc/min and an H gas flow of I74 cc/min. on a L68 mil carbon monofilament. The gas flows All of the Coatings consisted of adherent essentially were: methane 597 cc/min, BCl 74 cc/min and H 74 amorphous single phase carbon-boron alloy having a cc/min to yield a CHJBCL, ratio of8.08 and an H /Bcl composition at 48 atomic percent C. 52 percent B. ratio of L0. The monofilament was resistively heated Conditions and results are given in the following table.

TABLE ll CH /BCL, RalIo at Z 34 Final Avg. Current Voltage Power Temp Substrate Diam Speed LJTS Ex. (ma) (voltsj (Watts) (CI Diamlmil) (mil) (tt/hrl (psi! I2 2750 385 H00 3.: 3 l 50 195.000 I3 2750 413 11.15 do. 3.6 do. 240.000 i4 I700 :72 1190 do 4.2 an Ismiou I5 150 I750 261 1155 do. 4 0 30 270.000 (6 140 I950 271 11x5 l (10 4 i1 110 1.00110 17 lot) 1700 :7: 11m an 5.: 00 300.000 IK 130 2010 :1: 11.10 I (ix 4 4 (In 35x 0I11I l9 HIS I450 Is: 1140 (In 1 .10 :st nuw 20 1-10 I350 1115 11.7 -i 4 iii. ;'r.:. 1i0u It too 2500 Jso 1 t1, ll iln 3001100 22 I00 2135 3 1 |14 I It I4 11.- 307 00 TABLE II -Continued CH IBCI Ratio at 2.34

Final Avg.

Current Voltage Power Temp. Su bslratc Diam Speed UTS lzx. (ma) (volts) (watts) ("Cl Diamlmil) (mil) (ft/hr] (psi) 23 100 2275 22K H40 (10. 3.5 do. 308.000 24 I60 2400 334 l230/l l 85 do. 52 do. I65 .000 25* I 2675/2700 2.68 lIUU/I I50 do. 32 do. 297.000 26 I00 [440-] 6 l 0 I50 I I75 do. 3.4 do. 296.000 27 I00 I500 l50 1 I70 do, 3.2 do. 327.000

lndhiduul \alucs' as high as 400.000 psi.

(his flovi rates doubled tie. CH, at III-I ec/min. BCI, and H, each at 348 cc/min) '"Gas flow rates hahetl (in. CH. in 253 cclmin. BCI and H each at 87 cc/min] EXAMPLE 28 In the reactor apparatus of Example I, a CH /BCI ratio of l.l6 and an H /BCI ratio of L0 was maintained by a methane gas flow of 202 cc/min, a BCl gas flow of I74 cc/min and an H gas flow of 174 cc/min. A carbon-boron alloy coating was produced on a 1.36 mil Great Lakes Carbon monofilamentary substrate. The substrate was resistively heated utilizing I6l0 volts. I05 ma and I69 watts to ll85C while moving through the reactor at a rate of 40 ft/hr and achieved a final diameter of 42 mils. Several runs were made and the average UTS was 247,000 psi. The coating appeared to be an adherent single phase carbon-boron layer having a composition calculated to consist of 43 atomic percent C. 57 percent B.

Further experimentation was conducted at CHJBCI flow ratios both above and below those given for Examplcs l-28. At ratios higher than the 8.08 of Examples 1 and 2. the results were generally less satisfactory. In one series of experiments. for example. with a CHJBCI ratio of I015 and an H /BCl ratio of 1.0 maintained by a methane gas flow of 632 cc/min, a BCl gas flow of 62.3 cc/min and an H gas flow of 62.3 cc/min, seventeen separate runs of I68 mil carbon monofilament were made. Using parameter ranges of l-2l0 ma. ll60-2350 volts, 237-3I5 watts, l080-l [35C at speeds of 30-40 ft/hr. the coated filaments had a final diameter of 2.6-4.3 mils and a total average UTS of 99,000 psi. The coating was adherent single phase carbon-boron alloy with a composition consisting essentially of 64 atomic percent C, 36 percent B.

At a CH,/BCI ratio lower than l.l6, the results were unsatisfactory. In one investigation, for example, with a CH /BCI ratio of [.0 and an H lBCl ratio of 1.0 maintained by a methane gas flow of 252 cc/min. a BC];. gas flow of 252 cc/min and a hydrogen gas flow also at 252 cc/min. continuous runs could not be sustained because. with decomposition, there was severe embrittlement and consequent fiber breakage.

The carbon-boron coated carbon filaments are suitable for use in the reinforcement of not only resin, such as epoxy, but also metal matrices such as. for example. aluminum. magnesium and when properly coated. titanium and nickel. The filaments of Example l9 were subjected to testing in aluminum matrices. Composites were prepared by winding the coated fialment around 1 mil 2024 Al foil wrapped around a l2 inch diameter mandrel, spraying with polystyrene. removing from the mandrel and cutting into I X 5 inch pieces. A plurality of pieces (6 to 8) were laid up and diffusion bonded in a hot press at a temperature of 480C and pressure of I0,000 psi for 20 minutes. The resulting composite had a fiber loading of 45 vol. percent, a UTS of 98.000 psi and a Young's Modulus of 23 X l0..- psi.

By means of the present invention. it will be appreciated that a composite filament has been provided which significantly improves the potential utility of carbon in filament-reinforced structures. particularly insofar as the selection of matrix materials usable therewith is concerned.

What has been set forth above is intended primarily as exemplary to enable those skilled in the art in the practice of the invention and it should therefore be understood that. within the scope of the appended claims. the invention may be practiced in ways other thanas specifically described.

What is claimed is:

l. A composite filament at least two mils in diameter having a tensile strength of at least 150.000 psi for use as reinforcement in metal matrix composite articles comprising:

a substrate consisting essentially of carbon filament;

a continuous coating adhered to said substrate consisting essentially of carbon-boron alloy. said coating consisting essentially of approximately 43-60 atomic percent carbon. remainder boron.

2. The composite filament of claim 1 wherein said carbon filamentary substrate is at least one mil in diameter and said carbon-boron alloy coating is at least approximately /2 mil thick.

3. The composite filament of claim 1 wherein said alloy coating consists essentially of approximately 43-55 atomic percent carbon. remainder boron.

4. The composite filament-of claim 1 wherein said alloy coating consists essentially of approximately 48 atomic percent carbon, remainder boron.

5. The composite filament of claim 3 wherein said carbon filamentary substrate is at least one mil in diameter and said carbon-boron alloy coating is at least approximately Vz mil thick.

6. The composite filament of claim 4 wherein said carbon filamentary substrate is at least one mil in diameter and said carbon-boron alloy coating is at least approximately V2 mil thick. 

1. A COMPOSITE FILAMENT AT LEAST TWO MILS IN DIAMETER HAVING A TENSILE STRENGTH OF AT LEAST 150,000 PSI FOR USE AS REINFORCEMENT IN METAL MATRIX COMPOSITE ARTICLES COMPRISING: A SUBSTRATE CONSISTING ESSENTIALLY OF CARBON FILAMENT; A CONTINUOUS COATING ADHERED TO SAID SUBSTRATE CONSISTING ESSENTIALLY OF CARBON-BORON ALLOY, SAID COATING CONSISTING ESSENTIALLY OF APPROXIMATELY 43-60 ATOMIC PERCENT CARBON, REMAINDER BORON.
 2. The composite filament of claim 1 wherein said carbon filamentary substrate is at least one mil in diameter and said carbon-boron alloy coating is at least approximately 1/2 mil thick.
 3. The composite filament of claim 1 wherein said alloy coating consists essentially of approximately 43-55 atomic percent carbon, remainder boron.
 4. The composite filament of claim 1 wherein said alloy coating consists essentially of approximately 48 atomic percent carbon, remainder boron.
 5. The composite filament of claim 3 wherein said carbon filamentary substrate is at least one mil in diameter and said carbon-boron alloy coating is at least approximately 1/2 mil thick.
 6. The composite filament of claim 4 wherein said carbon filamentary substrate is at least one mil in diameter and said carbon-boron alloy coating is at least approximately 1/2 mil thick. 